Carbon Fiber vs Glass Wind Turbine Blades (1)

From its inception, the wind energy industry has had to fight to compete with other forms of electric power generation. Wind energy producers not only face that battle, but also wage war against each other for a competitive share in the wind market. Both battles boil down to a need to improve the economics of wind energy through increased energy capture. This has prompted a well-documented growth spurt in the size of turbines and rotor blades for land-based and offshore systems (see “Wind turbine blades: Big and getting bigger,” under “Editor’s Picks,” at top right). Offshore turbines are moving quickly from 3 MW to next-generation turbines rated at 5 MW and larger, on which blade lengths for both on- and offshore systems regularly exceed 45m/148 ft. As blades grow longer, the idea of converting structural areas of the blade from E-glass to significantly stiffer and lighter carbon fiber begins to make sense, despite the latter’s greater upfront cost.

Carbon fiber already has proven to be an enabling technology for turbine manufacturers Vestas Wind Systems A/S (Aarhus, Denmark) and Gamesa Technology Corp. (Zamudio, Vizcaya, Spain). Both companies embraced carbon fiber years ago, using it in select structural parts of their blades and taking advantage of the lighter weight blades throughout the turbine system. Lighter blades require less robust turbine and tower components, so the cascading cost savings justify the additional cost of carbon. “Vestas and Gamesa designed their turbines around the use of carbon fiber and, by virtue of that, the whole system cost is less than a system with an all glass-fiber blade,” confirms Dr. Philip L. Schell, executive VP of wind energy at carbon fiber manufacturer Zoltek Corp. (St. Louis, Mo.).

And that is before the increase in turbine efficiency that additional length enables. For example, the switch to carbon fiber enabled Vestas, initially, to add 5m/16 ft in blade length without any additional weight gain. The Vestas V112-3MW turbine is designed for low- and medium-wind areas and sports three 54.6m/179-ft blades. These blades have the same width as the company’s 44m/144-ft blades, but they sweep an area that is 55 percent larger. The result is considerably higher energy output.

More recently, GE Energy (Greenville, S.C.) joined the fray, specifying carbon fiber in its next-generation wind blades, including the 48.7m/160-ft blades for its 1.6-100 turbine. Yet, speaking at CompositeWorld’s 2011 Carbon Fiber conference in Washington D.C., Nirav Patel, senior lead engineer of GE Energy-Manufacturing Technology, issued a warning that carbon fiber cost and supply concerns could be showstoppers to further use of carbon fiber in GE applications. Patel also called for increased automation and improvements in manufacturing processes (see “What is carbon fiber’s place in wind energy systems?” under “Editor’s Picks”).

Notably, it may be GE’s use of carbon fiber to increase blade length on its 1.6-MW system that will ultimately push more wind energy companies to embrace carbon fiber. “GE’s decision to put a 100m [328-ft] diameter rotor on a 1.6-MW turbine has captured the attention of a lot of companies in the industry,” says Dr. Kyle Wetzel, president, Wetzel Engineering (Lawrence, Kan.), which designs wind turbines and rotors. “As a result, we are being approached by a number of companies that want to similarly upsize their machines.”